1. Field of the Invention
This invention relates to improvements in a control system for an occupant restraint system arranged to protect a vehicle occupant in the event of a vehicle collision.
2. Description of the Prior Art
A variety of control systems for an occupant restraint system have been proposed and put into practical use in the field of automotive vehicle. The occupant restraint system includes an airbag and/or a seat belt assembly to protect a vehicle occupant from coming into direct contact with a steering wheel and/or a windshield. One of typical control systems is disclosed in Japanese Patent Provisional Publication No. 4-50333 and arranged to operate the occupant restraint system to protect the vehicle occupant when an integrated value has reached a predetermined threshold value, the integrated value being obtained by integrating a deceleration of the vehicle detected by a deceleration sensor.
There are various kinds of vehicle collision modes. Examples of them are shown in FIG. 10 which illustrates a change in integrated value SG of a deceleration g in a vehicle collision. In the graph of FIG. 10, t0 indicates a timing at which the deceleration g exceeds a predetermined threshold value. This threshold value is provided to distinguish a vehicle collision from normal vehicle movements. Accordingly, there is a high possibility of occurrence of a vehicle collision when the deceleration g exceeds this threshold value, and therefore measurement and integration of the deceleration g is initiated from the timing t0.
In general, the integrated value SG of the deceleration g after initiation of the vehicle collision tends to first suddenly increase, then become generally constant, and thereafter again increase as shown in FIG. 10.
Now, the occupant restraint system is usually operated during a time period (t1 to t2) in which the integrated value SG of the deceleration g is generally constant. However, during such a period, the amount of change in the integrated value SG is considerably small as apparent from FIG. 10, and therefore it is required to precisely set threshold values THL1 and THL2. As a result, many troublesome adjustment operations are necessary for the control system.